Conventionally, there has been very generally used an immersion oil in a microscope field. When the immersion oil is optically used, compared with the case where the immersion oil is not used, a substantially small surface aberration can be obtained, and in addition, the immersion oil increases numerical aperture of objective lens and enhances magnifying power of a microscope.
As the immersion oil used in the above case, there are known: an immersion oil (e.g., refer to Patent Document 1) formed of a diarylalkane compound, a specific naphthalene compound, and a specific diphenyl compound; an immersion oil (e.g., refer to Patent Document 2) formed of benzylbutylphthalate and a chlorinated paraffin; an immersion oil for microscope (e.g., refer to Patent Document 3) containing a tricyclodecane derivative or containing, as a main component, a derivative of a substance having a basic structure of tricyclodecane; an immersion oil for microscope (e.g., refer to Patent Document 4) in which a liquid polybutene (liquid polybutylene) is compounded with a liquid aromatic compound having an ether bond; an immersion oil (e.g., refer to Patent Document 5) formed by compounding an aromatic compound into a liquid polyolefin; an immersion oil for microscope (e.g., refer to Patent Document 6) containing and/or hydrogenated product of a monomer to a tetrameter of norbornenes; an immersion oil for microscope (e.g., refer to Patent Document 7) in which a liquid diene copolymer is compounded with phthalate and paraffins; and an immersion oil for microscope (e.g., refer to Patent Document 8) in which a liquid diene copolymer is compounded with α-olefin.
The immersion oils have approximately sufficient characteristics required for an immersion oil for microscope, such as refractive index, Abbe number, viscosity, and resolution. However, the immersion oils are not sufficient in terms of persistence of low fluorescence at the time of determination by, for example, a spectrophotometer.
In general, a fluorescence microscope used for observing an object emitting fluorescence and the like is a microscope which is used for observing fluorescence emitted from a test body by irradiating the test body with excitation light such as UV light, and the fluorescence microscope has been utilized in various fields such as biology. In particular, a technology of a fluorescence microscope which detects an extremely weak fluorescence is being studied recently. In the case of detecting such a weak fluorescence, a high fluorescence, which is emitted from an immersion oil used for an optical system of a fluorescence microscope under UV light excitation, causes a noise when detected, whereby detection accuracy of the weak fluorescence becomes low. Studies of improving the immersion oil have been conducted relating to the above point, but further lower fluorescence and stable low fluorescence of the immersion oil have been demanded nowadays as described above, and the studies have not satisfied needs thereof yet.    Patent Document 1: JP 2623125 B    Patent Document 2: U.S. Pat. No. 4,465,621    Patent Document 3: JP 09-241214 A    Patent Document 4: JP 11-160623 A    Patent Document 5: JP 11-269317 A    Patent Document 6: WO 2004/090602    Patent Document 7: JP 2004-240245 A    Patent Document 8: JP 2004-240246 A